1. Field of the Invention
The present invention relates generally to rust-preventive agents and particularly to rust-preventive agents that are effective with iron and/or copper metals.
2. Description of the Prior Art
Conventionally used rust-preventive agents for iron and iron base alloys include materials such as sodium nitrite, organic and inorganic phosphoric acid compounds and their salts, and chromium-containing compounds, including simple and complex chromates. These agents, however, suffer various drawbacks. For example, sodium nitrite is a suspected carcinogen because it reacts with a means to produce nitroso compounds which are believed to be involved in the development of cancer in animals. Also, as chromium containing compounds exhibit toxicity due to the presence of chromium ions, and since phosphorous compounds offer an undesirable nutritive medium, the employment of these compounds as rust preventive agents has been accordingly limited.
Despite the above, sodium nitrite is widely used as a rust-preventive agent for iron and its alloys, as there is no such strongly effective water soluble agent available. While sodium nitrite is effective with iron and its alloys, it does not possess the comparable rust or corrosion inhibitive capability with respect to copper and copper base alloys. The result of the deficiency is that, in the instance where iron-copper alloys are to be treated for rust prevention, sodium nitrite offers limited protection to the metal.
A further drawback in the use of sodium nitrite is its limited useful life when disposed as a coating on the metal base. Sodium nitrite may be dissolved by the attack of certain microorganisms, and resultingly a coating containing this rust-preventive agent looses its effectiveness.
Other rust-preventive agents, include aliphatic acids, including aliphatic carboxylic acids. These materials, however are inferior as rust-preventive agents and are not widely used. Other known rust-preventive agents for copper-containing materials include benzotriazole, and its derivative, 2-mercaptobenzothiazolate and related compounds. These materials, however, have not exhibited rust-preventive capability with iron and iron-containing alloys.
A need therefore exists for a rust-preventive compound which offers a broad spectrum of capability with respect to both iron and copper-containing metals and at the same time exhibits extended effective life in solution.